RCD tripping under high load on 2 circuits

[Simonw586]

I’m in desperate need of someone with great fault finding knowledge. I have a dual rcd consumer unit as seen in picture. The left hand side rcd trips when anything with a high output like a tv for example is turned on in any sockets protected by the left rcd. The left rcd also trips when trying to switch on any light switches also protected by this rcd. The left rcd also trips if I use an appliance in the kitchen which is protected by the right hand side rcd, the appliances still work in the kitchen but they trip the left rcd and the rcd will not reset until I turn off whatever I’m using in the kitchen. I have had an electrician come round to investigate who left still scratching his head and told me that a full test would need to be carried out on the consumer unit as the faults were not pointing to one specific thing as 2 circuits are tripping the left rcd and not just 1. My house is 4 years old and I have owned it since new, one problem I have had since owning the house is the bath leaks onto the living room ceiling. I’ve had the builders out twice for this but that problem still persists. It has been like it for 4 years so I’m not sure if it has finally caused a problem? To summarise, any high output appliance used in the sockets protected by the left rcd trips the left rcd and also the light switches protected by the left rcd trip the left rcd. Everything in the kitchen works but using them causes the left hand rcd to trip. I have switched the rcd units with each other to eliminate the possibility of an over sensitive rcd but it made no difference so I have now swapped them back. I have checked the wiring on the sockets and light switches protected by the left rcd but couldn’t see any damage/loose connections. Any advice would be greatly appreciated as I’ve been trying to diagnose this problem for a week without any proper testing equipment. Kind regards, Simon

 

[telectrix]

Ha, ha, I’ve just noticed my spell checker converted you into a famous singer, sorry about that !

that's nothing .Once I had to text an Eastern lady customer, named Alka. when the text had gone, I noticed that the predictive text had called her AlkaSeltzer. She was not amused.

 

[Lucien Nunes]

it looks like there is no neutral on the outgoing side of the right hand RCD

It does look exactly like that, but I can't see how it can be. Circuits on the R/H RCD work, so that neutral bar must be correctly connected as the line appears to be. As there appear to be at least two neutral jumpers in the main switch outgoing terminal, not having one in the RCD would mean four cables disappear down behind the DIN rail but only three emerge underneath. It seems unlikely that someone would have left one unconnected, or put three in the main switch which I think we'd be able to see, so all the evidence points to this being a trick of the camera angle and in fact the neutral output link from the R/H RCD is sharply bent over towards the back of the CU just hidden by the RCD body.

 

[Simonw586]

Hi all, thank you for your replies, the problem has now been resolved. It was a cable that had been crushed in the loft supplying the first floor lighting circuit. The neutral had been crushed exposing the wire onto the earth wire. Strange how this was causing the sockets to trip the rcd also but the main thing is it’s fixed!

 

[Wilko]

And Sinatra has been rediscovered .

 

[Lucien Nunes]

Strange how this was causing the sockets to trip the rcd also

Thanks for reporting back, glad it's fixed. That behaviour might seem odd but electrically it's exactly what one would expect. The N-E fault on the lighting circuit will cause an imbalance in the RCD whenever there is any potential difference between N & E at the CU to drive current through it. That includes voltage drop due to loads on both different circuits on the same RCD, and loads on the other RCD, even loads next door if the supply is TN-S. The amount of load needed to cause a trip depends on how close to the supply the meeting point is between the faulty circuit and the load. Hence, small lighting loads on the faulty circuit itself would trip it, but on the other RCD only heavier loads such as the cooker would do so.